The invention relates to a manipulator comprising an end effector displaceable by means of a four-rod mechanism, two of the four rods being rotatable about a main axis extending perpendicularly to the plane in which the displacement of the four relatively rotatable rods takes place.
In a manipulator of the kind mentioned in the opening paragraph known from European Patent Application EP-A1-0232930, to which U.S patent application Ser. No. 198,618 filed 5/20/88 corresponds, the four rods of the four-rod mechanism are tubular throughout the entire cross-section and substantially throughout the entire length of the rods. The rods are coupled to each other at the area of four pivot axes parallel to the main axis. This means that the rods, which have to be coupled to each other, should be very accurately aligned or registered at the area of the connections between the rods in order to avoid stresses in the construction.
In practice, such constructions must be adapted to fit after the manufacture of the parts to be interconnected due to the fact that the fully tubular rods are kinematically overconstrained.